Explanation from NBA Official:
"Alright, when the play happened [James] Harden goes in for a dunk, and then the ball appears to pop back up through the net. When that happens, that is basket interference. To have a successful field goal it must clear the net. We have since come in here and looked at the play. He dunked it so hard that the net carried it back over the rim a second time, so in fact it did clear the net and should have been a successful field goal. As to could the play have been reviewed. It is a reviewable matter, but you have a window of 30 seconds to challenge the play during that timeout that he had and while they were protesting the call, trying to get clarification of it, that window passed so therefore it elapsed and they were not able to do it."